"S Mode" and forcing more of your Windows 10 application installs to use the Microsoft Store is a big one. A lot of the biggest culprits for the start time "things to finish" were ad hoc updaters from various terrible vendors.
Everyone: don't install Flash (built in to IE/Edge, if you need it, and you likely don't), don't install Java as much as you can avoid it (find alternatives or standalone installs), and install iTunes only from the Microsoft Store if you want it (goodbye Apple Updater, you will not be missed).
Those recommendations alone take care of so much startup gunk.
Power Users: check Startup applications and Services in Task Manager's Advanced/Details view from time to time. Task Manager in Windows 10 lets you disable Startup applications directly without needing any other tool. Many third party services you can switch from Automatic to Automatic (Delayed Start) and lose no functionality, but get out of the Windows startup "hot path". I have backup software that absolutely needed to be (Delayed Start), not just because it was slowing Windows startup but also because it was trying to access system/network resources before Windows was ready for them anyway, yet the installer did not default it to be (Delayed Start) up until just recently. (If you build Windows Services, consider defaulting your service installers for Delayed Start or Trigger Start. You don't need to be in the startup hot path, you are more likely to be getting in the way.)
Everyone: don't install Flash (built in to IE/Edge, if you need it, and you likely don't), don't install Java as much as you can avoid it (find alternatives or standalone installs), and install iTunes only from the Microsoft Store if you want it (goodbye Apple Updater, you will not be missed).
Those recommendations alone take care of so much startup gunk.
Power Users: check Startup applications and Services in Task Manager's Advanced/Details view from time to time. Task Manager in Windows 10 lets you disable Startup applications directly without needing any other tool. Many third party services you can switch from Automatic to Automatic (Delayed Start) and lose no functionality, but get out of the Windows startup "hot path". I have backup software that absolutely needed to be (Delayed Start), not just because it was slowing Windows startup but also because it was trying to access system/network resources before Windows was ready for them anyway, yet the installer did not default it to be (Delayed Start) up until just recently. (If you build Windows Services, consider defaulting your service installers for Delayed Start or Trigger Start. You don't need to be in the startup hot path, you are more likely to be getting in the way.)